1. Field of the Invention
The present invention relates to a ribbon microphone unit and a ribbon microphone in which damage on a ribbon diaphragm due to impact applied to the ribbon microphone unit and the ribbon microphone during transportation and upon installation is either prevented or reduced.
2. Description of the Related Art
A ribbon microphone mainly includes a pair of magnets for forming a magnetic field and a ribbon diaphragm. The magnets in pair are arranged in parallel at both sides of the ribbon diaphragm while being apart from the ribbon diaphragm for a certain space. The magnets form a magnetic field therebetween in which the ribbon diaphragm is arranged. The ribbon diaphragm is generally formed of an aluminum foil having a thickness of several micrometers. Aluminum is suitable as a material of a ribbon diaphragm of the ribbon microphone because its conductivity is better and its specific gravity is lower as compared with those of other metal materials. The ribbon diaphragm is held at both end portions in the length direction with an appropriate tension applied thereto while being apart from each of the magnets for a certain space. The ribbon diaphragm vibrates in the magnetic field upon receiving sound waves to make a current according to the sound waves flow in the ribbon diaphragm and the sound wave is converted into an electric signal.
FIGS. 5 and 6 illustrate an example of a conventional ribbon microphone unit. In FIGS. 5 and 6, the ribbon microphone unit has a frame 7 having a shape of a rectangular frame that is long in the vertical direction. A pair of permanent magnets 4 is fixed to inside surfaces of the frame 7. The permanent magnets 4 are disposed at respective sides of the frame 7 along the length direction with a certain space therebetween. The permanent magnets 4 are polarized in the width direction (right/left direction in FIG. 5). The polarizing directions of the pair of permanent magnets 4 are the same and a parallel magnetic field is formed between the permanent magnets 4.
A ribbon diaphragm (hereinafter, simply referred to as ribbon) 1 serving both as a diaphragm and a conductive material is disposed inside the parallel magnetic field. The ribbon 1 is an elongated belt-shaped member of which both end portions in the length direction are fixed to respective electrode lead-out portions 18 provided in both end portions in the length direction of the frame 7. The electrode lead-out portions 18 are insulated from the frame 7. Terminal plates 9 are fixed to the respective electrode lead-out portions 18. The end portions 11 of the ribbon 1 are held between the terminal plates 9 and holding members 8 by screwing the holding members 8 into the respective terminal plates 9 with screws 10 in a state where an appropriate tension is applied to the ribbon 1. Thus, the electrode lead-out portions 18 are electrically conductive via the ribbon 1.
The ribbon 1 is formed into triangular waves with the portion other than the end portions 11 corresponding to the electrode lead-out portions 18 alternately folded along lines in a width direction across the entire length at fixed intervals. The direction of the lines formed by the folding, that is, the direction of the lines drawn by the mountains and the valleys of the triangular waves is in the width direction of the ribbon 1. The lines are formed at fixed intervals.
The ribbon 1 vibrates upon receiving sound waves and traverses a magnetic flux between the permanent magnets 4. The ribbon 1 made of conductive material generates an electric power by traversing the magnetic flux and an electric signal is generated between both ends of the ribbon 1 in the length direction, that is, between the electrode lead-out portions 18. Since the electric signal has a frequency and an amplitude corresponding to those of the vibration of the ribbon 1, the sound wave applied to the ribbon 1 is converted into an electric signal corresponding to the sound wave.
In the ribbon microphone, which is a bidirectional mass control type microphone, the tension applied to the ribbon 1 is very low to set a resonance frequency of the ribbon 1 to a low-band frequency. The low tension is achieved by alternately folding the vibrating portion of the ribbon 1, i.e., the portion of the ribbon 1 other than the end portions 11 along lines in a width direction across the entire length at fixed intervals to form triangular waves as described above.
The ribbon 1, which is applied with low tension by being formed into rectangular waves with its vibrating portion being alternately folded, deforms due to inertia force attributable to the mass of the ribbon when the impact force is applied on the microphone. This leads to the degradation of frequency characteristic and malfunctioning of the microphone. Thus, ribbon microphones need to be improved in this point. FIGS. 7 to 10 explain the mechanism of the deformation. When impact force is applied in the horizontal direction, i.e., the direction parallel to the sound wave receiving surface of the ribbon 1 as shown in FIG. 7, the ribbon 1 deforms in the direction according to the impact force as shown in FIG. 8. The ribbon 1 does not deform if the folded portions indicated by the arrows in FIG. 9, i.e., the mountain portions and the valley portions in the triangular wave, are not unfolded. Folded portions in a conventional ribbon deform because no countermeasures have been taken to prevent the unfolding.
The folded portions of the ribbon 1 deform largely at the side opposite from that to which the impact force is applied and folded portions at either of the left and right sides are extended due to plastic deformation. In other words, the shape of the ribbon 1 becomes unsymmetrical due to the plastic deformation with different stresses applied to the left and the right of the ribbon 1. Once this happens, the ribbon 1 cannot return to its original shape and the resonance frequency is shifted to degrade the frequency characteristics. The ribbon 1 deformed over a certain level may be in contact with the permanent magnet 4 that is supposed to face the ribbon 1 with a certain space therebetween. This degrades the frequency characteristics and may cause malfunctioning of the whole system.
A ribbon microphone is transported, for example, while being incorporated in a box filled with and surrounded by a cushion to prevent an impact force from being directly applied to the microphone. However, no countermeasure has been taken for an impact force applied at a situation other than transportation such as a case where the ribbon microphone is accidentally dropped upon being mounted on a microphone stand upon installation.
The inventor has filed various patent applications related to a ribbon microphone unit, a ribbon microphone, and a method for manufacturing a ribbon for a ribbon microphone, part of which are disclosed in Japanese Patent Application Publication 2009-135630 and Japanese Patent Application Publication 2009-105506. The inventions disclosed in Japanese Patent Application Publication 2009-135630 and Japanese Patent Application Publication 2009-105506 are relatively similar to the present invention.
However, no countermeasures for effectively reducing the damage caused on the ribbon due to impact force is included in the inventions disclosed in Japanese Patent Application Publication 2009-135630 and Japanese Patent Application Publication 2009-105506.